Polycyclic Aromatic Hydrocarbons In Sewage Sludge Research Articles

The occurrence characteristics, removal efficiency, and risk assessment of polycyclic aromatic hydrocarbons in sewage sludges from across China

Sewage sludge is considered to be an important sink for polycyclic aromatic hydrocarbons (PAHs) in wastewater treatment plants and the potential risks from sludge contaminated with PAHs during land application has attracted attention. To identify the priority PAHs for control and enhance their removal from sludge, the occurrence characteristics, removal efficiency, and risk assessment of PAHs in sewage sludges from across China were analyzed. Data collection was from 2001 to 2023. Results showed that 16 PAHs were widely detected in Chinese sewage sludge with total amounts (∑16PAHs) between 0.06 and 34.93 mg kg dw−1. Fossil fuel, coal, and biomass combustion are main anthropogenic sources of PAHs in China. In general, phenanthrene (PHE), anthracene (ANT), fluorescein (FL), chrysene (CHR), pyrene (PYR), and benzo[b]fluoranthene (BbF) are regarded as the main components and PAHs with 3–5 rings dominate (84.01%–91.53%) sewage sludge in China. Although aerobic composting and anaerobic treatment significantly improve ∑16PAHs removal, sludge stabilization treatment only reduced the risk by a small amount, especially for high-molecular-weight (HMW) PAHs. The benzo[a]anthracene (BaA), benzo[a]pyrene (BaP), and dibenzo[a,h]anthracene (DahA) are proposed as the priority control contaminants for sewage sludge in China because they have consistently high-risk quotient (RQ) values of 2.42–7.47, 1.28–3.16, 1.06–1.83 before and after sludge stabilization, respectively. More attention should be paid to BaA, BbF, benzo[k]fluoranthene (BkF), BaP, DahA, and indeno[1,2,3-cd]pyrene (IcdP) in Beijing; ANT, BaA, and BaP in Shanghai; and BaA and BaP in Guanghzou. Although the toxic equivalent quotient (TEQ) for PAHs met the limit concentration requirements of the national standard, the potential health risks due to long-term exposure to HMW PAHs cannot be ignored because the incremental lifetime cancer risk (ILCR) was consistently in the risk threshold range (>1 × 10−6). Some suggestions on enhanced treatment approaches and land use standards are proposed to further alleviate the risk from HMW PAHs.

Distribution and ecological risk of polycyclic aromatic hydrocarbons in wastewater treatment plant sludge and sewer sediment from cities in Middle and Lower Yangtze River

The objective of this study was to conduct a comparative study of the distribution and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in the sewage collection and treatment system of four cities located in the middle and lower reaches of the Yangtze River. The results revealed that the mean concentration of 16 ΣPAHs was higher in the sewer sediments (1489.45 ng·g−1) than in the sewage sludge (781.78 ng·g−1). PAH monomers were detected in all cases, with higher mean Pyr, Chr, BbF and BaP concentrations. PAHs with 4–6 rings were dominant in both sewage sludge and sewer sediment monomer PAHs. With the isomer ratio method and positive definite matrix factor (PMF) method, the results showed that the major sources of PAHs in sewage sludge were petroleum sources, coal tar, and coking activities, whereas PAHs in sewer sediments were primarily from wood combustion, automobile emissions, and diesel engine emissions. Of all the PAH monomers, BaP and DahA had the highest toxic equivalents, although their levels were not the highest. Based on the assessment of ΣPAHs, it was concluded that both sewage sludge and sewer sediments had medium ecological risk. The results of this study provide reference information for the control of PAHs in the wastewater collection and treatment system of the middle and lower reaches of the Yangtze River.

Determination of Polycyclic Aromatic Hydrocarbons (PAHS) in Sewage Sludge and Compost by Dispersive Solid-Phase Microextraction (SPME) and Ultra-High Performance Liquid Chromatography (UHPLC) with Diode Array Detection (DAD)

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic that may degrade human health. Organic solvents are commonly used for the extraction of PAHs from solid samples and the analytes are determined chromatographically. This study describes the ultra-high performance iquid chromatography-diode array detection (UHPLC-DAD) determination of PAHs in sewage sludge and compost used as agricultural fertilizer. The PAHS may be transmitted to humans through the food chain. Analytes in the fertilizer were quantitatively extracted into the organic phase in water-dichloromethane-acetonitrile and determined liquid chromatographically. 16 PAHs were selectively extracted in a single clean-up step. For method development, the type and volume of organic solvent, pH of the water, and ultrasonic extraction time were optimized. For method validation, analytical figures of merit were obtained for the linearity, limit of detection (LOD), limit of quantification (LOQ), stability, intra- and inter-day precision, and accuracy. The developed and validated method was used for PAH determination in the fertilizers. Sample analyses were performed with 89–102% recovery values and 0.7–4.1% relative standard deviations.

Evaluation of the adsorption efficiency of carcinogenic PAHs on microplastic (polyester) fibers—preliminary results

Paper presents the results of investigations on sorption capacity of selected carcinogenic polycyclic aromatic hydrocarbons (PAHs) on microplastics fibers. Accumulation of organic micropollutants such as PAHs is indicated as one of the important problems in the case of microplastics present in surface water, including sea water. Concentrations of the micropollutants can reach even several mg/kg of microplastics. An unrecognized problem are sorption capacities of microfibers towards PAHs. Recent research works indicate that microfibers are commonly present in sewage sludge. Content of the fibers in this waste material can reach over 23000 particles per 1 kg of sludge dry matter. The fibers mainly come from cloth washing. It is obvious that the adsorption capacity of the fibers can affect the concentration of PAHs in sewage sludge. The aim of the study was to evaluate sorption capacities of polyester fibers towards PAHs. Adsorption of PAHs were provided under static conditions. After 24 h of adsorption 1255 μg/g of carcinogenic PAHs was adsorbed onto the polyster fibers. Amount of 6-ring PAHs was equal to 154 μg/g, whereas 5- i 4- ring ones, 562 and 539 μg/g, respectively. The results have confirmed that hydrophobic PAHs can be adsorbed onto polystyrene fibers and as a result cumulate in sewage sludge.

Polycyclic aromatic hydrocarbons (PAHs) persistence, bioavailability and toxicity in sewage sludge- or sewage sludge-derived biochar-amended soil

Soils can be contaminated with polycyclic aromatic hydrocarbons (PAHs) when either sewage sludge (SSL) or biochar (BC) are used. There are no comparative studies regarding the effects of soil amendment with SSL or BC on the persistence, bioavailability and toxicity of PAHs. This research compared the persistence of PAHs (based on the extractable content, Ctot) and their bioavailability (freely dissolved, Cfree) as well as the toxicity (solid phase: Phytotoxkit F with Lepidium sativum and the Collembolan test with Folsomia candida; leachates: Phytotestkit F with L. sativum and Microtox® with Aliivibrio fischeri) of soil amended with SSL or with SSL-derived BCs. BCs were produced from three different sewage sludges at a temperature of 500 °C. SSLs or BCs were added to the soil at a rate of 1% (30 t/ha). Adding SSL to the soil increased more the PAH content in it than after BC application, which was associated with a higher content of PAHs in SSL. Losses of Σ16 Ctot and Cfree PAHs were higher than those observed for biochar only in the case of one SSL. In the other cases, PAH losses were either higher for biochar or did not differ significantly between SSL and BC. On the other hand, the analysis of the individual groups of PAHs showed significant differences between SSL and BC, both for Ctot and Cfree. Nonetheless, these differences were largely driven by the type of sewage sludge and biochar. Only in the case of root growth inhibition the toxicity higher was for the SSL-amended soils than for the BC-amended ones. In the other cases, varying results were observed which were determined by the type of sewage sludge/biochar, similarly to PAH losses.

Bioleaching conditioning increased the bioavailability of polycyclic aromatic hydrocarbons to promote their removal during co-composting of industrial and municipal sewage sludges

Conditioning treatments are extensively employed in wastewater treatment plants (WWTPs) to enhance sludge dewaterability, thereby improving the sludge dehydration during mechanical dewatering. However, it remains unclear whether the sludge conditioning treatments would influence the removal of polycyclic aromatic hydrocarbons (PAHs) during the dewatered sludge composting. In this study, the influences of three sludge conditioning methods, including bioleaching conditioning driven by Acidithiobacillus ferrooxidans, chemical conditioning with Fe[III]/CaO, and chemical conditioning with polyacrylamide (PAM), on the bioavailability of PAHs in dewatered sludge and the PAH removal during the co-compositing of industrial and municipal sewage sludges were investigated. The results showed that bioleaching conditioning was capable to significantly increase the bioavailability of PAHs in dewatered sludge, which was not attained by the other two conditioning methods. During the 39 days composting of dewatered sludge, the total removal efficiency of six detected PAHs (∑PAHs) including acenaphthylene, fluorene, phenanthrene, anthracene, chrysene and benzo(k)fluoranthene was 58.7% in raw sludge, 58.5% in PAM-conditioned sludge, 76.4% in bioleached sludge, and 60.4% in Fe[III]/CaO-conditioned sludge, respectively, and the removal of acenaphthylene, chrysene and benzo(k)fluoranthene was much higher in bioleached sludge than in other sludges. During dewatered sludge composting, PAHs may mainly be degraded by the bacteria belonging to the genera Luteimonas, Glutamicibacter, Alcanivorax, Dechloromonas, Ferribacterium, Truepera and Sphingobacterium. Linear correlation analysis between PAH removal and their bioavailability revealed that the promoted PAH removal during the composting of dewatered bioleached sludge may ascribe to the enhanced bioavailability of individual PAH. Therefore, the combination of bioleaching conditioning and subsequent dewatered sludge composting is effective to remove PAHs in sewage sludge, thus alleviating the loads of PAHs during the land application of sludge compost products.

Comparison of PAHs uptake by selected Monocotyledones and Dicotyledones from municipal and industrial sewage sludge.

The study was focused on two goals: (i) the confirmation of the existence of a general relation between the content of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge and in plants growing in it, regardless of the type and content of sewage sludge, and (ii) if so, the answer to the question whether the uptake of PAHs by plants depends on their type. To realize the set aims, the contents of PAHs in four differentiated plant species were measured, two belonging to the Monocotyledones and two belonging to Dicotyledones group, growing in municipal and industrial sewage sludge in two locations. All the investigations were carried out during the period of 3 years. The results clearly demonstrated that the uptake of PAHs by a plant depended on polyaromatic hydrocarbon concentration in the sewage sludge. The relation between accumulation coefficient of PAHs in plant material vs. the content of PAH in sewage sludge was of exponential character. The results indicate that in case of four- and five-ring PAHs, the root uptake mechanism from soil solution occurs, regardless of the type and origin of sewage sludge and the type of plant. For three-ring PAHs, we can assume for Monocotyledones that the root uptake mechanism occurs because we observe a significant correlation between the content of fluorene, phenanthrene, and anthracene in plant material and in the sewage sludge. For Dicotyledones, the correlation is insignificant, and in this case probably two mechanisms occur—the uptake by roots and by leaves.

PAHs content of sewage sludge in Europe and its use as soil fertilizer

The European Commission has been planning limits for organic pollutants in sewage sludge for 14years; however no legislation has been implemented. This is mainly due to lack of data on sewage sludge contamination by organic pollutants, and possible negative effects to the environment. However, waste management has become an acute problem in many countries. Management options require extensive waste characterization, since many of them may contain compounds which could be harmful to the ecosystem, such as heavy metals, organic pollutants. The present study aims to show the true European position, regarding the polycyclic aromatic hydrocarbons (PAHs) content of sewage sludge, by comparing the Italian PAHs content with European Union countries, and at assessing the suitability of sewage sludge as soil fertilizer. The FOCUS Pearl model was used to estimate the concentration of benzo [a] pyrene (B(a)Pyr), the most toxic PAH in soil, and its exposure to organisms was then evaluated. The simulated B(a)Pyr and PAHs, expressed as B(a)Pyr, concentrations in soil were much lower than the B(a)Pyr’s most conservative lowest observable effect concentration (LOEC) for soil organisms. Furthermore, the results obtained indicate that it is more appropriate to apply 5tha−1 sewage sludge annually than 15tha−1 triennially. Results suggest, the EU maximum recommended limit of 6mgkg−1 PAHs in sewage sludge, should be conservative enough to avoid groundwater contamination and negative effects on soil organisms.

The transformation of PAHs in the sewage sludge incineration treatment

The release of pollutants from sewage sludge in the treatment process is a worldwide tricky problem in the field of sludge treatment. In this paper, the release and reaction between monomers of polycyclic aromatic hydrocarbons (PAHs) in the sewage sludge incineration treatment were studied based on simulated experiments. The result indicates that the transformation may occurre between monomers of PAHs during their release in the treatment. Over 90% of total PAHs in sewage sludge are released at the the temperature of 300°C–750°C. The possible transformation of Naphthalene to indeno(1, 2, 3-cd)pyrene was related to the temperature of the treatment system. Here, we showed that the output rate of transformation reactions for indeno(1, 2, 3-cd)pyrene is 94% at 300°C. These findings, by identifying corresponding treatment conditions as well as techniques, can help to understand the reactions and control real outputs of PAHs in the treatment process.

Stabilization of sewage sludge by different biochars towards reducing freely dissolved polycyclic aromatic hydrocarbons (PAHs) content

The objective of the study was to identify the effect of various biochars on the content of freely dissolved (Cfree) PAHs in sewage sludge. Apart from the evaluation of biochars obtained from various materials, the study also included the determination of the effects of biochar particle sizes and biochar production temperature on their ability to bind PAHs in sewage sludge. Increase in biochar dose caused a gradual reduction of Cfree PAHs content, but only up to the biochar dose of 5%. Depending on the kind of initial material from which the biochar was produced, the reduction of Cfree PAHs content in sewage sludge varied from 17.4% to 58.0%. Both the temperature and the particle size of biochar had an effect on PAH free concentration reduction. Biochars characterised by a low polarity index (O/C or (O+N)/C) reduced the level of Cfree PAHs better than biochars with a higher polarity index value.

Optimization and validation of solid-liquid extraction and purification at low temperature of PAHs in sewage sludge

In this study, a method of solid-liquid extraction and purification at low temperature (SLE-PLT) to determine 16 polycyclic aromatic hydrocarbons (PAHs) in sewage sludge was optimized and validated. The analyses were performed by HPLC-UV. The extraction phase, homogenization procedure, influence of pH, ionic strength and clean-up of the extracts were optimized. Recoveries were higher than 63.4% for 11 PAHs. The correlation coefficients were greater than 0.99 and limits of detection and quantitation were less than 0.060 and 0.15 µg g-1, respectively. These values were lower than the maximum residue limits of PAHs established by European legislation. SLE-PLT proved a more practical, economical method with fewer steps compared to Soxhlet extraction (reference method) for PAHs in sewage sludge.

Risk Assessment of PAHs in Solid Residues from Supercritical Water Gasification of Sewage Sludge

In this study, the contents of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge (SS) and solid residue (SR) from supercritical water gasification of SS were analyzed and the pollution degree and human health risk with PAHs in SS and SR samples were determined. SR samples were collected from different reaction condition, according to different reaction temperature, time and water content. The results show that the contents of PAHs in SR samples were increased after gasification reaction, ranging from1541 to 8234.8μg/kg, and that the PAHs with 4-6 rings are major pollutants in the SR samples. Based on Nemero Index P, the classification evaluation shows that the SR samples almost exceed the light polluted. While, the health risk assessment according to Benzo [pyrene total potency equivalents present that the health risks from PAHs are acceptable for children and adults using the SR sample for agricultural land.

Behaviour of PAHs during sewage sludge fermentation in the presence of sulphate and nitrate

In this study, the changes of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge and supernatants during anaerobic digestion under nitrate- and sulphate-reducing conditions were investigated. NaNO 3 or Na 2 SO 4 were added to the mixed sludge in order to obtain denitrification and sulphate reduction conditions, respectively. Abiotic loses of PAHs simultaneously were observed. Abiotic samples (with sodium azide) were also prepared. All sludge samples (biotic and abiotic) were incubated at 35°C in the dark. PAHs concentration was determined before incubation, after 13 d and after 20 d of incubation. Quantification of 16 PAHs (EPA) was carried out by GC-MS. PAHs were determined both in sewage sludge and in supernatants. During hydrolysis of organic compounds (first phase of fermentation) in the control samples (in sewage sludge and in superna tants) the increase of PAHs concentration occurred (especially naphthalene and 3-ring PAHs). The concentration of 16 PAHs in sewage sludge was reduced by 30% on average under nitrate-reducing conditions after 20 d and by 32% on average under sulphate-reducing conditions, respectively. The effectiveness of reducing of individual hydrocarbons was different. The concentration of carcino genic PAHs in sewage sludge was reduced by 73% on average under nitrate-reducing conditions and by 79% on average under sulphate-reducing conditions, respectively.

Heavy Metals and PAHs in Sewage Sludge from Twelve Wastewater Treatment Plants in Zhejiang Province

To investigate the heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in sludge of twelve wastewater treatment plants (WWTPs) in Zhejiang province of China, and to assess their potential for land application. Sludge was collected from 12 WWTPs within the province. GC-MS and AAS were used to measure PAHs and HMs contents in sludge. Concentrations of HMs in most of the sludge samples were below the regulatory limits for the sludge to be used in agriculture in China with the exception of Zn in 2 sludge samples and Cd in 1 sample. All 16 PAHs, targeted by the USEPA agency, were found in the sludge from the twelve plants with a total concentration ranging from 33.73 mg kg(-1) to 82.58 mg kg(-1) (dry weight, d.w.). The levels of Sigma9 PAHs varied from 13.87 mg kg(-1) to 61.86 mg kg(-1) (d.w.) in the sludge, far exceeding the limitation value recommended by the Europe Union. The concentration and composition of PAHs in sewage sludge varied and depended mainly on the quantity and type of industrial wastewater accepted by the WWTPs. A significant relationship between the proportion of industrial wastewater received by WWTPs and the total content of 16 PAHs in the sludge was observed. PAHs have become one of the primary pollutants in sludge of Zhejiang WWTPs instead of HMs. It is, therefore, essential to reduce the contents of PAHs before the sludge can be used in agriculture through proper treatment.

Effect of Composting on Polycyclic Aromatic Hydrocarbons Removal in Sewage Sludge

Changes in the concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) identified by the US Environmental Protection Agency as priority pollutants were investigated during the composting process of sewage sludge mixed with rapeseed marc (9:1, weight base). Results showed that total PAHs concentrations of the sludge sampled in different seasons had far exceeded the accepted Europe Union cut-off limits for land application. Phenanthrene, fluorene and dibenz(a, h) anthracene were dominant PAHs in the sludge, accounting for 62.8~69.6% of the total amount of the 16 PAHs. Composting appeared to be an effective method for the removal of PAHs in sewage sludge. After 50 days of composting, a significant reduction of concentration of the total PAHs was detected as compared with the initial concentration in composting material. The significant relationship between the biodegradation of organic matter and the losses of Σ16 PAHs during composting indicated that microbial degradation was the key process responsible for the efficient removal of PAHs from the sludge. Among all tested PAHs, fluorene was the most recalcitrant and became the primary residual PAH in the composted material. The lower removal rate of fluorene during composting was a limiting factor for the potential land application of the sludge. Further studies are needed to enhance the removal of fluorene in order to achieve a safe utilization of this sludge.

Occurence of PAHs in Various Elements of Environment in Zabrze (Upper Silesia, Poland)

The Polycyclic Aromatic Hydrocarbons (PAHs) pollution state of the chosen town (Zabrze) of Upper Silesia, the most industrialised region in Poland, was presented. Zabrze is a town of medium size, having population twenty times bigger than a medium town polulation in Poland. In this study we determined the qualitative and quantitative composition of PAHs fraction separated from the following elements of environment: suspended dust, drinking water, soil and sewage sludge. The following analytical techniques were used: Soxhlet Extraction, Solid Phase Extraction, Gas Chromatography-Mass Spectrometry, Capillary Gas Chromatography and High Performance Liquid Chromatography. The results confirmed the significant state of examined region pollution. They stated the exceed of contents B(a)P in suspended dust. The soils in that place were heavily polluted with PAHs, about 4000 µg · kg-1 for the sum of PAHs. The total contents of PAHs in sewage sludge of Zabrze did not exceed the analogous contents published for West European sewage sludge treatment plants and the level of determined PAHs in drinking water did not show any claims.